Studies conducted under this project are directed toward enhancing basic knowledge of the hormonal control of the growth process. Inherent differences in growth rate will be correlated with differences in embryonic and post-natal levels of blood and pituitary growth hormone, utilizing two strains of turkeys which differ markedly in rate of growth, length of the growth period, and mature body size. The inherent ability of pituitaries from fast- and slow-growing animals to secrete growth hormone in vitro will be studied, as will the response of these tissues to hypothalamic hormones. The ability of growth hormone to influence growth rate and body size in vivo will be studied through administration of exogenous growth hormone, growth hormone releasing and release-inhibiting factors, and anti-growth hormone serum globulin during embryonic development and early post-natal life.